Fracture Failure Assessment And CTOD Allowable Value Of E47 Steel Based On BS7910

Marine engineering equipment as a strategic development of China’s emerging industries,has gradually become a key issue in the field of marine structure research,and improving the level of marine structural safety testing is one of the key links.Most of the marine engineering structural damage accidents are caused by the sudden brittle fracture of the structure under harsh conditions.Therefore,it is very important for the structural steel to carry out the failure assessment process before service.In this paper,the container ship steel E47 as the object of study,in accordance with the BS7910:2013 latest version of the failure to assess the contents of the standard,the breaking resistance of the base material and the welded joint specimen was examined.Based on the principle of"combining with the use",the research on the fracture failure assessment of the structure includes four aspects:CTOD（Crack Tip Opening Displacement）test,simulation,normative evaluation and software development.At the same time,the method of CTOD permissible value optimization based on this criterion is proposed.The main research contents are as follows:1)Introduce the development background of CTOD test and the research status of BS7910 standard,which shows that CTOD test is the most effective method to measure fracture toughness of steel in structural standard.The evaluation of BS7910standard based on CTOD test can make the evaluation process more concise and scientific.2)The testing process of low temperature CTOD test on E47 steel is described,and the CTOD fracture toughness of E47 steel base metal and weld joint specimens with the thickness of 76 mm was measured.The results show that CTOD test technology can be effectively used to determine the BS7910 standard in the relevant assessment parameters.3)Introduce the relationships among δ₅ method,fracture mechanics parameters and finite element method,and expound the basic principle of finite element δ₅ method.Based on the CTOD test data,the_udand δ_m samples with different fracture types in the CTOD test were used to solve the crack tip stress by finite element δ₅ method respectively.This process can improve the method of calculating the abscissa stress ratio of the sample evaluation point（FAD）in the failure evaluation curve of the BS7910 standard.4)The CTOD test data and the finite element δ₅ method were used to evaluate the fracture toughness of E47 steel in BS7910 standard and to study the influence of correction on the assessment results.The low temperature CTOD test samples were used as the evaluation object in the three types of base metal,weld center and heat affected zone,According to the first-level assessment process,the abscissa stress ratio is obtained before and after the correction.The results show thatthe evaluation result is changed in some of the specimens after the abscissa stress ratio corrected.The evaluation point is moved from the unacceptable area to the acceptable area,and the evaluation degree is reduced.5)In order to solve the problem of the difference on CTOD allowable values in some standards,this paper establishes the calculation method of CTOD allowable value for specific samples according to the results of specimen fracture toughness evaluation.The definite step is to solve the change of the critical fracture toughness ratio of specific specimen before and after the correction,and the CTOD allowable value is determined by the ratio relation.Finally,the CTOD allowable value of specific specimen is solved according to the standard value provided.6)Based on the assessment process of fracture toughness and the optimization method of CTOD allowable value,the fracture assessment software on the BS7910:2013 standard is established,which can make the calculation process more effective and simple.